[petrochemist]

Paul
I definitely recomend the screw in models over the Lee/Cokin style. IR filters block so much light that the stray light round the back of the filter will cause problems.

I've managed to get some very cheap IR filters from China (via e-bay) which seem to work perfectly. A range of sizes & transmittion wavelengths are available, if you're not sure if your camera is suitable I think one of these is the best approach to give it a try, though postage might take a few weeks.

I'll be travelling close past you next week on my way to/from a course (Wednesday morning/Thursday early evening), and could let you have a play with my filters if that would help. (I've got two 52mm filters & a 49mm one, but should be able to find some stepping rings too if required).